1. Field of the Invention
The invention relates to display devices. More specifically, the invention describes a method and apparatus for enhancing the appearance of motion on an LCD panel display.
2. Overview
Each pixel of an LCD panel can be directed to assume a luminance value discretized to the standard set [0, 1, 2, . . . , 255] where a triplet of such pixels provides the R, G, and B components that make up an arbitrary color which is updated each frame time, typically 1/60th of a second. The problem with LCD pixels is that they respond sluggishly to an input command in that the pixels arrive at their target values only after several frames have elapsed, and the resulting display artifacts—“ghost” images of rapidly moving objects—are disconcerting. Ghosting occurs when the response speed of the LCD is not fast enough to keep up with the frame rate. In this case, the transition from one pixel value to another cannot be attained within the desired time frame since LCDs rely on the ability of the liquid crystal to orient itself under the influence of an electric field. Therefore, since the liquid crystal must physically move in order to change intensity, the viscous nature of the liquid crystal material itself contributes to the appearance of ghosting artifacts.
In order to reduce and/or eliminate this deterioration in image quality, the LC response time is reduced by overdriving the pixel values such that a target pixel value is reached, or almost reached, within a single frame period. In particular, by biasing the input voltage of a given pixel to an overdriven pixel value that exceeds the target pixel value for the current frame, the transition between the starting pixel value and target pixel value is accelerated in such a way that the pixel is driven to the target pixel value within the designated frame period. In order to calculate an overdrive voltage for a particular frame, the overdrive algorithm stores previous frame data (in a non-recursive type algorithm) or predicted frame data (in a recursive type algorithm) in a memory device (such as a SDRAM). Incoming frame data is then compared with the stored frame data and the overdrive values are calculated. The new calculated overdrive data will then be output as new data display on the LCD and the stored frame data (in SDRAM) is updated by the previous frame data (non-recursive) or predicted frame data (recursive).
Unfortunately, however, by improving the response time of the LCD panel, the overdrive technique also allows low-level noise (typically calculated as a difference between observed luminance values between adjacent video frames, or portions thereof) that would otherwise not be visible to become perceptible on the LCD panel as image artifacts. Such noise may appear as a rippling effect in static fields or jitter associated with even slowly moving objects. This is due, in part, to the fact that a by decreasing the response time of the LCD panel, the low-level noise artifacts are preferentially enhanced.
Therefore what is required is a method, system, and apparatus for selectively applying an LCD overdrive techniques that avoids enhancing low level noise artifacts.